Sean Keller, 4, laughs at his brother Liam, 8, while reading a book Tuesday with his sister Amelia, 11, in their home in Marengo. Sean was diagnosed with acute lymphoblastic leukemia in August. Bears player Devin Hester will be signing autographs in Crystal Lake on July 21 to raise money in support of the Keller family.

MARENGO – There’s really only one question 4-year-old Sean Keller has before he meets Chicago Bears wide receiver Devin Hester later this month.

“He’s like, ‘How big is he? Is he bigger than Daddy?’ That’s what he wants to know,” Sean’s mother, Val Keller, said with a laugh.

Little Sean Keller of Marengo was diagnosed nearly a year ago with acute lymphoblastic leukemia. Later this month, he will meet the NFL’s all-time leader in punt return touchdowns during a charity event.

Hester will sign autographs July 21 at Joseph’s Marketplace in Crystal Lake. The proceeds will go to Sean and the Keller family. The money will be used for a private pool party for Sean, and to pay for medical bills, as well as for car repairs and maintenance.

“We’re truly surrounded by such wonderful family and friends,” Val Keller said. “We’ve been given this wonderful gift of support from so many people we know, and people we don’t even know. It’s wonderful.”

Sean Keller is being treated at the University of Chicago Medicine Comer Children’s Hospital. He swallows about 20 medications each week, including daily oral chemotherapy treatments. He gets infusions once a month and spinal taps every three months.

The chemotherapy had stripped the little boy of his hair, but peach fuzz is beginning to grow back on his head. He calls it his “spring growth.”

But despite the intensive treatment, Sean Keller is a typical 4-year-old boy. He likes to play outside, go camping, kick a soccer ball, throw a football.

Sean Keller was about 3 1/2 years old when he was diagnosed in August. He was complaining of pain in his legs and had fevers that would come and go. His illness didn’t present itself as leukemia initially. He visited four hospitals and doctors told the Kellers that Sean’s sickness was merely a viral infection and sent them home.

But Val Keller and her husband, Michael, who both work for Centegra Health System, knew something wasn’t right.

Finally, they heard the words that are every parent’s nightmare: Their youngest child has cancer.

“That wasn’t even an option that crossed our minds ... that it would have been cancer,” Val Keller said. “We were told it was an 85 percent chance that it was not leukemia. You Google everything that it could be, but we didn’t Google that.”

But Sean’s prognosis looks good, and this fall he will start preschool at Zion Lutheran School in Marengo.

The Hester charity signing will start at 6 p.m. He will autograph any item for $79. Personal inscriptions are an additional $30. Professional photographs will be taken with Hester for groups of up to five people for $89.